 Additionally, mutations in the genes for myophosphorylase along with deoxyguanosine kinase have been associated with muscle glycogenosis and mitochondrial hepatopathy.The G456A PYGM mutation and duplication in exon 6 of dGK that results in a truncated protein have been associated with phosphorylase deficiency in muscle, cytochrome c oxidase deficiency in liver, severe congenital hypotonia, hepatomegaly, and liver failure.This expands on the current understanding of McArdle disease and suggests that this combination of mutations could result in a complex disease with severe phenotypes.